Phased array antennae are well known in the field of radio and microwave communication. They comprise a plurality of antenna elements spaced apart from each other by known distances. By applying a calculated phase shift to signals received or transmitted from each element, the antenna may effectively be steeredxe2x80x94that is, given a high gain in a certain direction. A phased array antenna typically comprises a planar array of elements, and the direction of maximum gain may typically be steered in two directions, which may be referred to as xe2x80x9cazimuthxe2x80x9d and xe2x80x9celevationxe2x80x9d for convenience. The maximum gain direction, or xe2x80x9cbeamxe2x80x9d may be steered within a particular angular range, dependent on the construction of the phased array. Typically, the range allows for the beam to be steered to any direction within 60xc2x0 of the normal to the plane of the array.
Such antennae find application in the fields of satellite communication, mobile telephony and microwave communication.
In a particular embodiment, the present invention provides a novel configuration of a phased array antenna for mobile satellite communications from an airborne platform.
Such antennae have limited angular range, as discussed above, and some attempts have been made to overcome this limitation. For example, it is desired to be able to send and receive communications to/from a particular satellite without having to realign the phased array antenna each time that a new satellite is to be communicated with. Similarly, if the phased array antenna is to be mounted on a moveable vehicle, one does not want to have to realign the antenna every time a transmission or reception is to take place.
U.S. Pat. No. 5,861,840 and European Patent Application 0 767 511, each incorporated herein by reference, each describe an antenna array for providing wide angle coverage, using a number of planar phased arrays. In an example described in these documents, triangular planar arrays of dipole antennae are formed using a method similar to printed circuit board manufacture. Thirty triangular arrays are assembled into a polyhedron providing substantially hemispherical coverage. Each planar array is capable of being steered so as to transmit and/or receive signals within an angular range of up to about 60xc2x0 from the normal. The invention described in U.S. Pat. No. 5,861,840 and European Patent Application 0 767 511 is based on placing a number of such planar arrays in mutual proximity, angled to each other at angles of less than about 60xc2x0. By providing enough planar arrays, one may be sure that at least one of the planar arrays will be capable of satisfactorily receiving and/or transmitting in a required direction.
While U.S. Pat. No. 5,861,840 and European Patent Application 0 767 511 provide an antenna composed of a number of component planar arrays arranged in an approximate hemisphere, or other polyhedron determined by the required coverage, such antenna assemblies may be impractical in certain situations. For example, while it may be possible to mount a hemispherical or even spherical antenna assembly on a mast carried by a land vehicle or water-borne vessel, it may be impractical to mount such a mast, or indeed such an antenna array, on a high-speed vehicle such as an aircraft.
The present invention therefore aims to provide a relatively omnidirectional phased array antenna which is conformal, that is, may be adapted to be mounted on a carrying vehicle without substantially negatively influencing the aerodynamics or aesthetics of the contour of the vehicle. The present invention applies particularly to aircraft, since issues of aerodynamics are of great importance. Furthermore, the aircraft, and hence any attached antenna array, may change its orientation with respect of the source or destination of the radio signal, in roll, pitch and yaw. It is important that the antenna array can remain in communication with the radio source/destination despite such movement of the antenna.
Although suitable for mounting on an aircraft, the antenna array of the present invention may find application to other vehicles, such as water-borne craft, which may also move in roll, pitch and yaw, although to a lesser extent than aircraft, and to land vehicles which move principally only in yaw (azimuth), but may need hemispherical coverage to remain in communication with one or more communications satellites at certain elevation angles, while the vehicle moves in azimuth.
Accordingly, the invention provides apparatus and methods as defined in the appended claims.
In particular, the present invention provides an antenna assembly comprising a plurality of planar tiles. Each of the tiles carries a planar array of sets of antenna elements arranged to be operated as a phased array antenna, the tiles being arranged in an orientation which is conformal to a contour of an underlying structure.
The underlying structure may be a part of a vehicle carrying the antenna structure, such as a part of the fuselage of an aircraft or a part of a superstructure of an aircraft. The underlying structure may alternatively be a part of a land vehicle or a water-borne vehicle.
In a certain embodiment, the tiles are arranged in a first arc about an axis. The tiles are then each arranged in a plane tangent to the arc. Preferably, the planes of the tiles are parallel to the axis. A further arc of tiles may also be provided about the axis, each tile of the further arc being tilted with respect to the adjacent tile of the first arc, towards the axis. In a certain embodiment, a further arc of tiles about the axis, is provided on each side if the first arc of tiles, each tile of each further arc being tilted with respect to the adjacent tile of the first arc, towards the axis.
Preferably, in such embodiments, the angle of the tilt is sufficient to enable the antenna array to be sensitive in the direction of the axis. The angle of the tilt is preferably at least approximately 30xc2x0.
Each tile may comprise control circuitry for controlling phase shifts in signals applied to, or received from, each set of antenna elements.
The present invention also provides a method of communication, comprising the steps of:
providing an antenna assembly as described;
calculating a direction of required transmission/reception with respect to the antenna assembly;
calculating which of the tiles are capable of transmitting or receiving in the required direction;
enabling the capable tiles and disabling the remaining tiles;
steering the antenna elements of the enabled tiles in the required direction; and
using the enabled tiles of the antenna array for transmission and/or reception of required signals.